When a 911 emergency center receives a call, the ability to accurately locate the caller can dramatically affect the degree of success emergency personnel have in responding to the need for help. Dispatching the emergency personnel to the correct location is crucial to administering help as quickly as possible. When a person dials 911 from a traditional wireline telephone, the emergency center identifies the number of the wireline telephone and cross-references that number with an address database to determine the location of the wireline telephone, and thus the location of the caller.
Wireless telephones, however, are not fixed in a single location and therefore are not associated with any particular address. Thus, without a means for determining the location of the mobile wireless telephone, the emergency center must rely on the caller's knowledge and communication of her location, which often leads to errors. The inability to determine the location of a wireless caller is compounded by the fact that an increasing number of 911 calls are coming from wireless telephones. Indeed, studies indicate that approximately 45 million Americans made 911 calls from wireless telephones in the year 2000. In some areas, wireless 911 telephone calls account for fifty to seventy percent of the call volume coming into public centers.
Recognizing the need to automatically determine the location of wireless telephone callers, in 1996, the Federal Communications Commission required wireless network operators to have the ability to determine the location of wireless 911 callers by October 2001. As a result, wireless operators have developed what are generally referred to as enhanced 911, or E911, services. These services typically identify the latitude and longitude (i.e., x and y coordinates) of a wireless device that is making a 911 call.
E911 services help ensure that wireless telephones provide 911 call centers, or Public Safety Answering Points (PSAPs), with the vital information necessary to locate and identify a caller in an emergency. The E911 standards promulgated by the Federal Communications Commission (FCC) require wireless network providers to track the location and identity information of all wireless callers, with the purpose of providing such information to emergency personnel when a caller dials 911 from a wireless telephone.
Under the FCC rules, wireless networks and the corresponding wireless handheld devices, such as cellular telephones, will provide both the identity and location of the caller to a 911 dispatcher. To provide a caller's identity, the wireless handheld device will furnish a device identification, e.g., a mobile identification number (MIN), indicating in most instances the telephone number of the device. The wireless network and wireless handheld devices will provide the location of callers using a network-based location system (e.g., triangulation), global positioning systems (GPSs) within the handheld devices, or a combination of the two systems.
When conventional E911 systems provide only a longitude and latitude for a wireless device, the systems assume that a device could be found at only one possible altitude of that location. Thus, for example, given x-y coordinates corresponding to a soccer field, emergency responders can assume that the wireless device is on the soccer field at the reported x-y coordinates. As another example, given x-y coordinates corresponding to a single-level highway, emergency responders can assume that the wireless device is on the highway at the reported x-y coordinates.
In many situations, however, buildings and irregular topography provide several different altitudes or elevations at which the wireless device could be located on the same x-y coordinates. For example, in a skyscraper, the same x-y coordinates could correspond to a device located on the first floor or the eightieth floor. An emergency responder arriving at the skyscraper, knowing only the x-y coordinates, would therefore be unable to quickly determine on which floor the emergency is occurring.
FIG. 1 illustrates this skyscraper problem, in which a coordinate X,Y within the footprint of building 100 is reported by the E911 location service. That particular coordinate X,Y could correspond to a device anywhere along the axis Z for the entire height H of building 100. Thus, the taller building 100 is, the more difficult it is to determine the exact location (i.e., altitude) of the calling wireless device.
As another example, on an interchange between major highways, several roads and ramps may pass under and over each other. The same x-y coordinates could correspond to a device located, for example, on the lowest road or a bridge passing high above. Knowing only the x-y coordinates, an emergency responder would have to guess on which road the emergency is occurring.
FIG. 2 illustrates this situation, in which a first road 200 passes underneath a second road 202. A particular coordinate X1,Y1 is reported by the E911 location service. However, as shown, that particular coordinate X1,Y1 could correspond to a point on road 200 at a first altitude A1 or to a point on road 202 above at a second altitude A2. Thus, knowing only the coordinate X1,Y1, an emergency dispatcher does not know whether to send responders to road 200 or road 202.